Technologies have recently been developed that enable information to be transmitted to electronic devices by means such as television and print media. For example, U.S. patent application Ser. No. 10/673,047, filed on Sep. 26, 2003 and entitled “Block-Based Encoding and Decoding Information Transference System and Method,” and U.S. patent application Ser. No. 10/618,445, filed on Jul. 11, 2003 and entitled “Interactive Electronic Commerce and Message Interchange System,” both of which are hereby incorporated by reference, disclose methods and systems that enable the transmission of a message carrier within a stream of video and television data. This message carrier is subsequently captured by an electronic device and decoded to identify a message code. The message code facilitates financial transactions and data interchange, as well as dissemination, management and exchange of commercial information, for example, advertising, promotions, sales announcements, and the like. The message carriers and message codes are disseminated through advertising and content from analog and digital television broadcasts, television receivers, the Internet, wireless signals, satellite broadcasts, and print media.
In the above referenced patent applications, the message carrier is typically captured by a Universal Digital Assistant (UDA), such as a personal digital assistant (PDA), using a digital camera. The UDA captures a digital image of a television screen displaying the message carrier, and software methods are then used to analyze the digital picture and resolve the message code contained in the message carrier. As disclosed in U.S. patent application Ser. No. 10/673,047, the message carrier can be an image composed of blocks representing data that is shown on a television screen (e.g., as shown in FIG. 1). These blocks can vary in color and/or intensity to convey the data. For instance, this block-based encoding scheme can use low-intensity blocks to represent one bit value and high-intensity blocks to represent another bit value.
Unfortunately, complications can arise when capturing a digital image of a message carrier that is being shown on a television or computer display. A digital camera uses an image sensor, such as a charge-coupled device (CCD) or a complementary metal-oxide semiconductor (CMOS) sensor, to capture a digital image. The image sensor is generally composed of thousands of photosites that receive light passing through the lens of the digital camera. This light is converted into electrical charges by the photosites and there is a limit to how much charge each photosite can store. If there is too much charge for one photosite, the charge will overflow to neighboring photosites causing a two-dimensional inter-symbol interference (ISI) effect which is called image blooming or streaking.
Conventional digital camera images generally do not suffer from blooming effects because the light captured by the photosites is simply ambient light reflected by subjects within the image. Unlike conventional images, a digital image of a television or computer display is more susceptible to blooming or inter-symbol interference effects because these displays are transmitters of light, and do not simply reflect ambient light. The large amount of light transmitted by a television or computer display, especially from white or high-intensity regions on the display, can easily overload one or more photosites of an image sensor, thereby inducing the blooming effects. If such blooming effects occur within a message carrier, the integrity of the data being conveyed can be corrupted or destroyed. Specifically, this blooming effect can obscure or blur the transitions between the low-intensity bits and the high-intensity bits in the block-based encoding scheme discussed above (e.g., as shown in FIG. 2), rendering it more difficult, and in some instances impossible, to detect these transitions and decode the message carrier.
Another complication we have mentioned that can arise when capturing a digital image from a television or computer display is called intersymbol interference (ISI). In a digital transmission system, intersymbol interference refers to distortion of a received signal, that distortion being manifested in the temporal spreading and consequent overlap of portions of the signal to the degree that the receiver cannot reliably distinguish between changes of state, for example, between individual signal elements. Similar to blooming effects, ISI can blur transitions between low-intensity bits and high-intensity bits.
Accordingly, methods are needed to minimize the effect of blooming and ISI when capturing digital images of message carriers being shown on television or computer displays.